All internal combustion engines, except those operating under Diesel cycle principles, require an ignition spark to initiate the combustion of the compressed fuel/air mixture. Several methods of generating said ignition spark are presently well understood. They all rely upon the rapid imposition of a high voltage, of the order of ten or twenty kilovolts, across the gap of a "spark plug," which is caused to arc across said gap producing a spark. These systems differ in the manner in which the high voltage is supplied to the spark plug, the means utilized to produce the high voltage, and in the primary source of the electrical energy.
For convenience in relating the several methods currently in use with the invention disclosed herein, the primary source of electrical energy will be limited to magneto devices, such as are typically used in motorcycles and similar applications.
The most common approach presently in use, in its simplest form, employs a set of mechanically actuated breaker points and a capacitor configured in a parallel circuit with a low voltage output magneto, and that group in parallel circuit with the primary winding of a standard ignition transformer. The secondary winding of the ignition transformer bridges the gap of the spark plug. The breaker points are abruptly opened, by the mechanical action of a cam, at or near the peak of the magneto output, thereby generating a voltage pulse of approximately 100 to 200 volts across the primary winding of the ignition transformer. This voltage is transformed into the required high voltage which appears across the secondary winding of the ignition transformer.
Such systems require frequent maintenance because of the severe arcing across the breaker points during the opening process. A capacitor is used to suppress much of the arcing, but the problem remains. Additionally, the cam surfaces wear rapidly and require lubrication. The performance of these systems suffers at high speeds due to the mechanical inertia of the breaker point assembly causing erratic timing. Moreover, the time available to build substantial energy in the magneto transformer is inversely proportional to the engine speed.
In order to overcome the disadvantages found in "breaker" type ignition systems, several "breakerless" techniques have subsequently been disclosed. These systems, often called "electronic ignition" or "capacitive discharge ignition" systems, all employ a capacitor wherein electrical energy is caused to be stored until it is rapidly discharged through the primary winding of the ignition transformer. Several alternate triggering techniques have been suggested but in operation they appear to be similar in that they rely upon either peak detection of the magneto output voltage or zero-crossing in the rate of change of magneto output voltage to provide a gate signal to a silicon-controlled rectifier or a similar device which then becomes conductive thereby allowing the capacitor to rapidly discharge.
Due to the characteristics of such capacitive discharge systems as are presently within the knowledge of the inventor herein, the primary energy source, typically a magneto, must produce a voltage output significantly higher than that required of a breaker type ignition system. This results in the necessity to produce specially wound magnetos having either a larger number of turns in the windings or extremely large and strong magnets, or some combination of the two. Such special magnetos, which will provide the higher voltages required to charge the capacitor, significantly increase the cost, weight, and volume of the ignition system.